1. Field of the Invention
This invention relates to an electromagnetic trigger device for use with a camera capable of automatic time exposure.
2. Description of the Prior Art
There has been proposed a cine camera of the type in which a motor is started by an electromagnet trigger device, which also controls the position at which a shutter is stopped, and a shutter driving mechanism for transporting a film and actuating a shutter mechanism is driven by the motor and which cine camera is further provided with a member for stopping the shutter at the position where the shutter is kept opened (to be referred to as the opened position) in order to attain the optimum exposure when a long exposure is required under the low or poor lighting condition such as the exposure at night or the microscopic photography, and a member for stopping the shutter at the position where the shutter is closed (to be referred to as the closed position hereinafter), whereby a long exposure may be attained by single frame exposure means for stopping the shutter in the opened position. The cine cameras of the type described are for instance disclosed in U.S. Pat. Nos. 3,721,492 and 3,722,989. However, with the system for permitting a long exposure of the type described in U.S. Pat. No. 3,721,492, when a release button is depressed for finishing a long time exposure, a shutter is closed, and the next frame is transported and successively the next exposure is initiated. Therefore, this exposure system is not advantageously adapted for use in, for instance, the microscopic photography for recording, for instance, the cell division or the growth of the crystal in which each frame must be exposed for a relatively long time, for instance 20 seconds, and the interval (to be referred to as the rest time hereinafter) between the successive two exposures must be also longer, for instance 5 minutes. The system disclosed in U.S. Pat. No. 3,722,989 is not advantageously adapted for use with conventional camera of the type operating on a battery because the system flows the current through an electromagnet for long exposure time. In both of the above systems, the exposure is manually made so that a user must operate the camera while measuring the exposure time and the rest time. Furthermore, it is very difficult for a non-skilled operator to set the optimum exposure time, and if the conditions are changed, a test exposure must be made. Thus both of the above systems are inconvenient in practice.